In recent years, mobile devices such as cell-phones (and in particular smart-phones), tablets and laptops have become ubiquitous. Most of these devices include one or two compact cameras: a main rear-facing camera (i.e. a camera on the back side of the device, facing away from the user and often used for casual photography) and a secondary front-facing camera (i.e. a camera located on the front side of the device and often used for video conferencing).
Although relatively compact in nature, the design of most of these cameras is very similar to the traditional structure of a digital still camera, i.e. they comprise an optical component (or a train of several optical elements and a main aperture) placed on top of an image sensor. The optical component (also referred to as “optics”) refracts the incoming light rays and bends them to create an image of an object or scene on the sensor. The dimensions of these cameras are largely determined by the size of the sensor and by the height of the optics. These are usually tied together through the focal length (“f”) of the lens and its field of view (FOV)—a lens that has to image a certain FOV on a sensor of a certain size has a specific focal length. Keeping the FOV constant, the larger the sensor dimensions (e.g. in a X-Y plane) the larger the focal length and the optics height.
As the dimensions of mobile devices (and in particular the thickness of devices such as smartphones) shrink, the compact camera dimensions become more and more a limiting factor on the mobile device thickness. Several approaches have been proposed to reduce the compact camera thickness in order to alleviate this constraint. One such approach uses a so-called “folded” camera module that includes a “folded lens”. In the folded camera module structure, an optical path folding element (referred to hereinafter as “OPFE”) e.g. a prism or a mirror, is added to tilt the light propagation direction from a direction perpendicular to the phone back surface to a direction parallel to the phone back surface. If the folded camera module is part of a dual-aperture camera, this provides a folded optical path through one lens module (normally a “Tele” lens module). Such a camera is referred to herein as folded-lens dual-aperture camera or dual-aperture camera with folded lens. Zoom dual-aperture and multi-aperture cameras with folded lens are disclosed for example in Applicant's US patent application No. 20160044250. A zoom dual-aperture camera with folded lens is also shown therein incorporated in a portable electronic device (e.g. a smartphone).
In addition to the optics and sensor, modern cameras usually further include mechanical motion (actuation) mechanism for two main purposes: focusing of the image on the sensor and optical image stabilization (OIS). For focusing, in more advanced cameras, the position of the lens module (or at least one lens element in the lens module) can be changed by means of an actuator and the focus distance can be changed in accordance with the captured object or scene. In these cameras it is possible to capture objects from a very short distance (e.g., 10 cm) to infinity. The trend in digital still cameras is to increase the zooming capabilities (e.g. to 5×, 10× or more) and, in cell-phone (and particularly smart-phone) cameras, to decrease the pixel size and increase the pixel count. These trends result in greater sensitivity to hand-shake or in a need for longer exposure time. An OIS mechanism is required to answer the needs in these trends. More information on auto-focus and OIS in a compact folded camera may be found in Applicant's international patent applications PCT/IB2016/052143 filed Apr. 14, 2016, PCT/IB2016/052179 filed Apr. 15, 2016 and PCT/IB2016/053335 filed Jun. 7, 2016.
In OIS-enabled cameras, the lens or camera module can change its lateral position or tilt angle in a fast manner to cancel the handshake during the image capture. Handshakes shift the camera module in 6 degrees of freedom, namely linear movements in orthogonal directions X-Y-Z, Roll (tilt around the X axis), Yaw (tilt around the Z axis) and Pitch (tilt around the Y axis). Henceforth and for simplicity, the terms “around the X axis”, “around the Y axis” and “around the Z axis” are replaced with, respectively, “around X”, “around Y” and “around Z”. The definitions of Roll, Yaw and Pitch as used in this description are shown with reference to FIG. 1, which shows an exemplary smartphone 100 in a front perspective view and a back perspective view, the back view showing two back cameras 102 and 104. Hereinafter, the undesirable Roll motion of the camera module resulting from handshakes or other unwanted movements may also be referred to (in addition to simply “Roll”) as “camera module-induced Roll movement” or “camera module-induced Roll”. “Roll” also relates to the tilt around the optical axis of the camera module that provides the displayed image. Roll results in rotation of an image around the image center (and may thus be referred to as “image Roll”). The linear motion in X-Y-Z has negligible effect on the image quality, and does not have to be compensated for.
FIG. 2 shows an embodiment of a folded camera module numbered 200 with both AF and OIS mechanisms, disclosed in Applicant's international patent application PCT/IB2016/053335. Camera module 200 comprises a lens module 202 carrying a lens, an OPFE (here a mirror) 204 and an image sensor 206. The lens may have for example a 4-20 mm effective focal length (EFL), serving as a “Tele” lens, and it can be included in a dual-aperture camera together with a second camera module having for example a lens with 3-5 mm EFL (“Wide lens”) and a second image sensor.
The lens module and the mirror move independently of each other, the movements shown by arrows. That is, lens module 202 may perform two movements, a movement for AF along the Z axis and a movement for OIS along the Y axis. Another movement for OIS is achieved by tilt of mirror 204′ around Y. The two movements for OIS compensate for Pitch and Yaw but not for Roll.
There is a therefore a need for, and it would be advantageous to have devices, systems and methods that compensate for image Roll in addition to Pitch and Yaw, particularly in dual-aperture or multi-aperture cameras that include a folded camera module and in host devices (such as smartphones) incorporating such cameras.